MT3608 boost converter module
The little blue MT3608 step-up module: 2 to 24 V in, and a trimmer sets the output above the input, up to 28 V.
Aliases: MT3608 boost, boost converter, step-up converter, DC-DC converter, voltage booster. The board carries Aerosemi's MT3608 switcher, a 22 uH inductor, an SS34 Schottky diode, a 22 uF capacitor on each side and a blue multiturn trimmer.
A boost converter is the buck converter turned round. It stores energy in the inductor from the input and lets it out on top of the input, so it trades amps for volts: one Li-ion cell at 3.7 V made into 5 V at 1 A takes about 1.5 A from the cell.
Pins
| Pin | What it does |
|---|---|
VIN+ |
The input, 2 V to 24 V. |
VIN- |
Input ground. |
VOUT+ |
The output, set by the trimmer, never below the input. |
VOUT- |
Output ground. |
VIN- and VOUT- are one copper pour on the board, so the ground goes straight
through: wire either one to ground and the other is ground too.
Properties
volts is where the trimmer is turned to, from 0.6 V to 28 V. The default is 12 V.
A real module comes set to whatever the factory left it at, often 20 V or more.
Set it with a meter on VOUT+ before anything is connected to the output.
While it runs
The readout is VOUT+ above VOUT-. Before Run it shows the trimmer's setting.
What the model gets right
The figures are from Aerosemi's MT3608 sheet, with the board's own parts.
Power in is power out plus the losses. The input current is the output's power plus what the switch (80 milliohm), the diode, the inductor and the switching edges lose, over the input voltage. From 5 V to 12 V at half an amp the model is about 90 % efficient, where these modules measure 88 to 93 %.
The output is never below the input. With the switch off, the inductor and the
diode join VIN+ to VOUT+. So a module set to 5 V on a 12 V input gives about
11.6 V, and one that is off, or under its 2 V input range, still passes its input
on less a diode drop. A boost converter is not a regulator that can step down.
The switch limit. The switch limits at 4 A, and the inductor carries the output
current over 1 - D, so what the converter can add to the output shrinks as the
ratio grows: about 1.6 A from 5 V to 12 V, about 0.7 A from 3.7 V to 20 V. Past it
the output sags. The board is sold as a 2 A module and gets hot long before that.
No short circuit protection. The limit caps what the converter adds, not what flows through the diode: a short on the output is a short on the input.
Ninety percent duty at most. The output cannot rise past about ten times the input.
What it does not model
The 1.2 MHz ripple (the output here is its average), light-load operation, soft start, the enable pin (tied on on the board), heat, and the inrush that charges the output capacitor through the diode when the input is first connected.
Common mistakes
Expecting it to step down. Set under its input, the output is the input less a diode drop, not the setting.
Not setting the trimmer first. A module set to 24 V on an Arduino's 5V pin kills the Arduino.
Too small a supply. A 5 V, 1 A output from 3.7 V takes 1.5 A from the battery; a coin cell or a 9 V battery cannot give that.